Casing head equipment for boreholes or wells



Nov. 20, 1934.

L.. M. c. sEAMARK 3 Sheets-Sheet 1 Invenvtor Attorney.

Nov. v20, 1934. L.. M. c. sl-:AMARK l1,981,431

CASING HEAD EQUIPMENT FOR BORE HOLES 0R WELLS Filed Nov. 27, 1931 3 Sheets-Sheet. 2

i Inventor l.' Hfen/mak'.

by In s. M441 `dtorney.

d a..d1a.c@4af1b1ce 3 d Fig.4.

Nov. 20, 1934. L.. M. C. sEAMARK CASING HEAD EQUIPMENT FOR BORE HOLES OR WELLS Filed Nov. 27, 1951 I 5 Sheets-Sheet 3 Attorney.

Patented Nov. 20, 1934 UNITED STATES CASING HEAD EQUIPMENT FOR BORE- HOLES R WELLS Lewis Mervyn Cecil Seamark, Chag'ford, England Application November 27, 1931, Serial No. 577,574 In Great Britain October 7, 193i.

Claims. (Cl. 16B-14) This invention relates to an equipment serving as an internal blow-out prevnt'er by which perforated or plain tubing may be inserted into bore-holes under pressure without killing the well as is usually done.

The invention is of special advantage when used with an external blow-out preventer or packer such as described in' the speciiication of the co-pending applications Serial No. 483,290 dated 20th September 1930, and Serial No. 560,993 dated 3rd September 1931; in the use of which anexternal joint may be made around the external surface of the tubing as it is passed into or withdrawn from the bore-hole.

5 According to the present invention an internal `ioint is made within the tubing as it is run into or withdrawn from the bore-hole, by an internal piugging or jointing device adapted to be held within the tubing in a convenient position cori@ responding to that of an external blow-out preventer surrounding the tubing, whereby a tight joint is maintained internally as lwell as ex- *rnally in the operation.

According to the invention moreover the lnternal plugging or jointing device is adapted to be held against the well pressure and in corresponding relation to the external blow-out preventer or packer mounted upon the well head. For the purpose a mandrel is provided in coe incident position above the well head, that is xedly held to resist the well pressure and over which lengths of tubing may be passed successively for connection together and to be snubbed into the bore-hole by means such' as commonly `5 used for the purpose.

According to the invention moreover the internal plugging or jointing device essentially comprises an elastic jointing sleeve or the equivaient, which is subject to the well pressure for o maintaining an effective joint, as well as to pressure mechanically applied, as for example by a split spring ring or cylinder in compression or a number of such ringsor cylinders one beside or within the other, that is or are adapted to apply pressure from within the elastic jointing sleeve outwardly.

According tov the invention moreover the elastic jointing sleeve is adapted to be carried by a cylindrical body part that at its upper end is 'provided with the means by which connection may be made with the lower end of the mandrel.

According to the invention moreover means are provided for the disconnection of the lower end of the mandrel from the internal plugging or jointing device, and for simultaneously locking the latter in position, whence it cannot be expelled under the well pressure.

The invention comprises constructional fea tures of the internal plugging or jointing device. Thus as a means of connection of the mandrel and the cylindrical body part and for locking the device in position when the mandrel is disconnected and withdrawn the invention comprises upstanding dogs of two or more in number set equidistant apart and above the cylindrical body part upon or beneath which the elastic jointing sleeve is carried. The dogs have recesses on their inner faces in line, into which a boss or-ange integrally provided at the lower end of the mandrel may enter when the dogs lie within the tubing. These recesses may have a rectangular cross section and may all serve also for mounting within the recesses and between the clogs split spring rings in compression by which all the dogs are normally thrust outwards. The dogs at or above a middle position extend outwardly to form an annular top face or shoulder that is adapted to engage beneath an inner annular ange or shoulder provided within a coupling sleeve or the equivalent which may be used to connect a length of plain tubing with the upper end of the last length of the perforated tubing inserted. The middle part of the coupling sleeve beneath the annular ange or shoulder .referred to may have a bore of a g5 diameter slightly larger than than of the tubing, whereby under the outward pressure of the split spring rings the dogs are pressed outward to assume their outermost position oncoming tolle within the coupling sleeve referred to. The upper ends of the dogs are reduced and have a conical outer face at their upper end of a barbed or hook shaped section; the dogs in the outer position they thus assume within the coupling sleeve release the boss or flange on the lower 95 end of the mandrel. The further snubbing-in of plain tubing may' thereupon proceed without the use of the mandrel having regard to the fact that the dogs in the outer position they assume within the coupling sleeve prevent the outward movement of the internal plugging or jointing device under the well pressure.

The invention comprises the further featuresA of the internal plugging or jointing device hereinafter described, as Well asl the features of method and apparatus that are' hereinafter referred to.

The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which Figure 1 is a vertical section of the internal plugging or jointing device constructed according to the invention.

Figure 2 is a detail plan view on the line 2--2 of Figure l.

Figure 3 is a detail plan of Figure l.

Figures 4 and 5 are sectional elevations of modifications in construction of the internal. plugging or jointing device.

Figure 6 is an elevation showing the manner of use of the internal plugging or jointing device illustrated in Figure l.

Figures 7 and il are plan views of the clamps and anchoring supports shown in Figure 6.

Figure 9 is a diagrammatic view illustrating the manner of use of the internal plugging or jointing device.

In carrying the invention into eect according to one construction the internal plugging or jointing device may consist ci acylindrical body view on the line 3--3 part u oi a diameter slightly less than the bore Y- of the perforated or plain tubing b to be inserted into the bore-hole, and beneath this body part a a cylindrical elastic jointing sleeve c may be applied upon a downwardly depending con centric tubular member d screw-threaded into a central hole within the body part d. The ci s tic sleeve cmay be provided with conical ems c1 c1 adapted to enter conical' recesses respective'A ly provided beneath the cylindrical body part a and upon a ring or washer e set upon the externally screw-threaded lower end of the concentric tubular member d and held in position by means of a nut el applied beneath.

The elastic jointing sleeve c is provided with an internal annular cavity c2 extending short oi the ends of the sleeve c, for the reception within of a perforated cylindrical sleeve 1*, and each of the ends f1 of the cylindrical sleeve f is advantageously provided conical to form conical cavities at each end around the tubular member d upon which the cylindrical sleeve fis applied so that thus the conical washer e on the tightening of the nut e1 beneath it serves to transmit pressure to the upper and lower ends of the elastic jointing sleeve c. The cylindrical sleeve f may advantageously be provided with' an internal annular cavity i? through which free passage is permitted, the cavity i2 extending short of the respective ends f1 of the sleeve f and with an external annular cavity f3 that is adapted for the reception of one or more split spring cylinders or rings g in compression. The latter is thus adapted to apply pressure outwardly upon the adjacent internal surface of the elastic jointing sleeve c. The cylindrical sleeve ,f is provided with transverse holes f4, and transverse holes d1 may also be provided in corresponding or other posi tion in the depending tubular member d, by which the well pressure may be transmitted to the inner face of the elastic jointing sleeve c, it being understood that the internal annular cavity c2 in the elastic jointing sleeve e allows of free communication from the holes d1 in the de- The upper end of the body part o'. is provided.

with a central hole a1 communicating with the central bore of the depending tubular member d, and at the lower end at a2 is provided with a seat for a valve it whose stem extends upward and has position of the lower end of the mandrel y' the noemer a helical spring h1 mounted on its upwardly protruding end. This valve h is thus adapted to be positively actuated by means of a rod for equal- Sil 'higher than that of the Well pressure, or of the pressure below the plugging or jointing device.

The upper face of the body a is provided with recesses a3 of anfalmost cylindrical form. These may for example be four in number and may be provided in two opposite pairs disposed parallel and equidistant from the centre and from each other for the accommodation of the lower ends oi two or more dogs i also set in parallel and oppositely disposed pairs having their lower ends i1 of partially cylindrical forni. The lower ends i1 of 'the dogs may thus eiter the recesses asin an axial movement and each of the ends i1 may be provided with a peripheral groove i2 with which the end of a grub screw i3 may engage as a simple means for ensuring xity oi? lateral position oi lthe respective dogs i, whereby the dogs may thus hinge or pivot upon their lower ends il while being held from lateral displacement.

The dogs i are' co-extensive in their upper ends i* they are reduc. have a corneal outer face i5, and in tion on their outer faces the rl-ogs wardly extending parts if. while in a ce ing position at their inner races an open t il lis provided advantageously oi a rectangular Jbrin. rThe lower face of these recesses i7 determines the recesses il are thus adapted for the reception of an outwardly extending boss or flange 7"; at the lower end of the mandrel :i by which the iixity of position of the internal plugging or jointing device is determined. 'I'he outwardly extending boss il lies against the lower inwardly extending `face or the recesses i7 formed at the inner faces of ing withdrawn from the bore-hole. ln this posi'l tion the recesses iI on the inner faces of the dogs i are engaged by the outwardly extending boss or flange il of corresponding form at the lower end of the mandrel i. The split spring rings k however cause the outward movement of the dogs z on the dogs passing into a coupling sleeve lhaving a larger internal diameter than the 'mternal diameter oi' the tubing b, whereby the outwardly extending parts oi the dogs i at their outer faces engage beneath an integral shoulder Z1 provided in the coupling sleeve and thus the outward movement oi the plugging or jointing device is prevented under the well pressure on the release oi' the lower end of the mandrel j on the outer pivotal movement of the dogs i in the manner described. By such means the outwa" Y'y extending boss or iiange i1 at the lower end ci ne mandrel y' clears the recesses i7 on the inner faces of the dogs i, and thus the withdrawal of the mandrel 7 is pern'iitted.

The mandrel j is provided of a length in excess of the lengths or sections of the tubing b, and at its respective ends i2, y? (Figure o) is advanta.- 150 geously provided with a buttress thread by which it may be held within suitable transverse clamps m n and anchoring supports for the purpose of xedly holding the mandrel'q in position above and coincident with the well head with the lower end of the mandrel 7' engaged in the manner described by the dogs i, the latter being set into such position that the plugging or jointing device beneath, assumes a position corresponding to the surrounding external blow-out preventer p.

For the purpose of inserting perforated or plain tubing b into the bore-hole the plugging or jointing device such as hereinbefore described is inserted into a length of the perforated or plain tubing b (Figure 6) with the lower -end of the 'mandrel y' engaged by the dogs i, and the length of tubing b carrying the plugging or jointing device and the inserted mandrel 9' may. be passed into the blow-out preventer p and into a.container p1 beneath, which is mounted upon the well head ange p2, a suitable valve p3 being interposed to isolate the container p1 from the well. The upper end of the mandrel :i may be secured by the transverse top clamp m and the upper end of the length of perforated or plain tubing b engaged by one of the clamps of the snubbing gear, whereupon the valve p3 on the well head is opened and the length of tubing b is snubbed-in. The connection and snubbing-in of further lengths of perforated tubing or plain tubing b may then proceed as is usual.

It will be understood that by such means the mandrel :i is held stationary as the tubing b is lowered into the bore-hole against the well pressure, and that a pressure tight joint is maintained between the elastic jointing sleeve c and the inside of the tubing b, and between the packing medium in the external blow-out preventer 'p and the'external surface of the tubing b. The external blow-out preventer p is preferably provided of a construction such as described in the specification led pursuant to the copending applications liereinbefore referred to in which the packing medium takes the form of a massive elastic sleeve d.

In the use of the internal plugging or jointing device, the device comprising the body a, the tubular member d and the elastic sleeve c and the dogs z', with the mandrel :i are inserted into a length of the perforated tubing b, the device With the mandrel y' and perforated tubing b are then inserted into the container p1 (Figure 9) mounted above the main valve p3 on the well head, the snubbing-in gear is then attached `to the tubing b, and a clamp m (Figure S) is attached to the top threaded part i2 of the mandrel 7', this clamp m being held by anchoring supports m1 and bolts m2. The plugging or jointing device is then set so that the elastic jointing sleeve c is opposite to the massive elastic sleeve or the` equivalent in the external blowout preventer p, the external blow-out preventer is closed on to the outside of the perforated tubing b and 'the main valve p3 on the well head is then opened. Thereupon the length of perforated tubing b, is snubbed-in untilthe lower thread i2 on the mandrel i is exposed, and the upper end of the perforated tubing b is then clamped in position, oy the bottom snubbing clamp of the snubhing gear to prevent it being blown out of the well. The clamp n is then put upon the lower threaded end :i2 of the inandrel i and this clamp n is then anchored to the adjacent anchoring support or clamp o on the partly inserted tubing b as illustrated in Figure 6. The clamp m by which the top threaded end 72 of the mandrel :i is vheld is then removed for the application of another length of perforated tubing b. This further length of tubing b is then loweredl over the top of the mandrel 7' and the clamp m secured to the upper screwthreaded end i2 of the mandrel 1. The clamp n at the lower threaded end 92 of the mandrel j is then removed. The additional length of tubing is then screwed into that already partly within the bore-hole. The snubbing-'in gear is thereupon attached to the upper end of the added length of tubing. The clamp is then removed from the upper end of the length of tubing previously snubbed-in and the further length of tubing is then snubbed into the well. The oper- 'ations are repeated until the required amount of perforated tubing has been snubbed-in.

'Ihe special coupling sleeve Z such as hereinbefore described provided centrally with a bore of a slightly larger diameter than the internal diameter of the tubing b may be connected at the top of the last length of the string of perforated tubing, 'so that thus when this coupling sleeve l reaches the dogs i, the latter move outwardly in a pivotal movement to release the lower end 71 of the mandrel 1' and to engage beneath the inwardly extending flange or shoulder Z1 within the coupling sleeve l. Thus also no further upward movement of the internal plugging or jointing device is permitted. The

remaining lengths of plain tubing may now be inserted without the use of the mandrel', and the internal plugging or jointing device being xedly set in position by the engagement of the dogs within the coupling sleeve, descends with the tubing.

It will be understood that the exposed internal bore of the other couplings used for connecting the sections of plain or perforated tubing are of insufcient length to accommodate the outwardly extending parts of the dogs i, which thus cannot move outwardly to release the end of the mandrel as the couplings passv the internal plugging or jointing device.

After the desired number of lengths of tubing have been inserted the pressure above and below the internal plugging or jointing device may be equalized by opening the valve h in the cylindrical body a thereof, or by pressure being applied to the How-head. The internal plugging or jointing device can now be tripped by dropping a go-devil down the bore-hole, whereby lthe tops of the dogs i are encircled and engaged by which they are forced inward for their i nev further be understood that by the application of 14@ It may also drawn until the outward pivotal movement of the dogs i is permitted on their passing into I in the manner described.

More than one internal plugging or jointing device or unit may be used with a view to provide against damage to the elastic jointing sleeve of one of them. Thus as illustrated in Figure 4 the downwardly. depending tubular member d of one unit may be extended substantially beneath the end nut for the purpose of the connection of a. further tubular member d upon which a second elastic jointing sleeve c may be mounted with an internally applied cylindrical sleeve ,f as hereinbefore described. 'I'he connection of the lower tubular member d may be effected by means of a cylindrical collar q having a conical face q1 on its underside, and the respective tubular members d at their lower ends may be provided with a.

- series of holes d3 by which the fluid pressure methe other in the manner described, and each may be equipped at its upper end with a valve such as l h as illustrated in Figure 5, that is adapted to` be opened on a higher pressure applied above the which an effective joint may be maintained should one of the units of the device fail. For this Lpurpose near the lower end of each ofthe down- -wardly depending tubular members d of each unit a non-return ball valve q3 or the equivalent may be mounted in such manner than an enclosing space is provided within the bore of thedownwardly depending tubular members d, which is thus adapted for the upward passage only of a iiuid pressure medium. Thus should the elastic jointing sleeve c of the upper unit be damaged the fluid pressure medium may pass between the tubing and the sleeve of the upper unit, thence through the holes d3 in the downwardly protruding end of the tubular member d of the iirst unit for passage through the valve h in the upper end of the tubular member d of the second unit, whereby a pressure may be imposed under which an effective joint may be made of the elastic jointing sleeve with the inside of the tubing, while where the elastic jointing sleeve of the first unit is unimpaired, the uid pressure medium may pass through the valve h at the upper end of the ilrst unit to maintain a pressure within the elastic jointing sleeve of the iirst unit. By such means the internal plugging or jointing device at the surface and the elastic jointing sleeves may be caused to pack oil eectively should one or more of themfail.

It will be understood however that the use of a single unit with a ball valve or the Aequivalent in the lower end of the tubular member may be employed.

It will furthermore be understood that an elastic jointing sleeve of india rubber may be used, but no limitation is imposed to that inaterial.

I claim:-

1. An internal plug for tubing in pressure wells comprising a cylindrical elastic jointing sleeve, the internal cylindrical surface of which is exposed to the well pressure and mechanical means at the well head above the internal plug by which the internal plug is iixedly located and held within the tubing against u'pward'axial thrust-under the well pressure during the running-in or withdrawal of the tubing.

2. An internal plug for use in pressure walls comprising a body part, a cylindrical elastic jointing sleeve upon the body part, and means at the well head above the internal plug by whichv the body part is mechanically located and held within the tubing to resist upward axial thrust under the well pressure4 during. the running-in or withdrawal of the tubing.

3. A blow-out preventer for use in pressure wells comprising a well head casing, tubing adapted to extend into the well, an external packer Within the casing, the external packer having an internal cylindrical elastic jointing sleeve externally exposed to fluid pressure. and being adapted for the passage through it of the tubing, and

an internal plug within the tubing, the internal plug having' an external elastic jointing sleeve internally exposed to the well and means by which the internal plug is adapted `to be xedly held at the well' head to resist axial thrust under the well pressure during the running-in or withdrawal of the tubing. 1

4. A blow-out preventer for use in pressure wells comprising a well head casing, tubing adapted to extend into the well, an external packer within the casing, the external packer having an internal cylindrical elastic jointing sleeve externally exposed to iiuid pressure and being adapted for the passage through it of the tubing, an internal plug 'within the tubing, the internal plug being adapted to be set within the tubing in concentric and coincident relation with the external packer in the well head casing, the said internal plug having an external elastic jointing sleeve internally exposed to uid pressure,

means by which the internal plug is adapted to be ilxedly held at the well head to resist axial vthrust under the well pressure during the running-in or withdrawal of the tubing, and means internal cylindrical elastic jointing sleeve externally exposed to iiuid pressure and being adapted for passagethrough it of the tubing, an internal plug within the tubing, the internal plug having an external elastic jointing sleeve internally exposed `to the well, and mechanical means at the well head for xedly locating and holding against upwardnthrust the internal plug within the Itubing under the well pressure during the running-in or withdrawal of the tubing.

6. An internal plug for tubing in pressure wells, comprising a. body adapted for release from engagement at the well head and for free axial movement within the tubing, a cylindrical elastic jointing sleeve upon the body and means within the body by which the internal cylindrical surface of the sleeve is always exposed to the well from below the body.

7. An internal plug for tubing in pressure wells, comprising a body adapted for release from engagement at the well head and for free axial movement within the tubing, a cylindrical elastic jointing sleeve upon the body, means within the body by which the internal cylindrical surface of the sleeve is always exposed to the well from below the body, and means at the well head by which the body and sleeve are mechanically located and held within the tubing in the operation of running-in or withdrawal of the tubing.

8. An internal plug for tubing in pressure wells, comprising a body adapted for release from engagement at the well head and for free axial movement within the tubing, part of which body is of tubular form and open at the lower end, and a cylindrical elastic jointing sleeve upon the tubular part, and means by which the internal surface of the sleeve is subject to the pressure of the well consisting of holes extending through the tubular part.

9. An internal plug for tubing in pressure wells, comprising a body adapted for release from engagement at the well head and for free axial movement within the tubing, a cylindrical elastic jointing sleeve upon the body, means within the body by which the internal cylindrical surface of the sleeve' is exposed to the well, and a valve at the upper end of the body, the valve being normally thrust upward into its closed position and being adapted to open in a downward movement on pressure applied 'to the valve from above the said body.

10. An internal plug for tubing in pressure wells, comprising a body adapted for release from engagement at the well head and for free axial movement within the tubing, part of said body being of tubular form and open at the lower end, a cylindrical elastic jointing sleeve upon the tubular part, the tubular part having holes therein extending therethrough by which the said sleeve `is subject to the well pressure from below the body, and a valve at the upper end of the body normally closed and adapted to be open in a downward movement on pressure applied. to the valve from above the said body.

11. An internal plug for tubing in pressure wells, comprising a body, a cylindrical elastic jointing sleeve upon the body, the sleeve being at its ends formed with inwardly extending conical edges and having an internal annular cavity extending short of its respective ends, the cavity having conical end faces forming recesses of an acute angled cross-section, an internal cylindrical sleeve of a form corresponding to the cavity and tting therein, means for the application of axial pressure at one end of the elastic `iointing sleeve, and means within the body and within the internal sleeve by which the internal cylindrical surface of the elastic jointing sleeve is exposed to the' well. l

12. An internal plug for tubing in pressure wells, comprising a body, a cylindrical elastic jointing sleeve upon the body, the sleeve being at its ends formed with inwardly extending conical .edges and having an internal annular cavity extending short of its respective ends, the cavity having conical end faces forming recesses of an acute angled cross-section, an internal sleeve of a forni corresponding to the said cavity and fitting therein, annular recesses on the internal and external faces of the internal sleeve, the recesses extending short of the respective ends thereof, means for the application of axial pressure at one end of the elastic jointing sleeve, and means within the body and in the internal sleeve by which the internal cylindrical surface of the elastic jointing sleeve is exposed to the well.

13. An internal plug for tubing in pressure wells, comprising a body, a cylindrical elastic jointing sleeve upon the body having an internal annular cavity extending short of the ends of said sleeve, an inner cylindrical sleeve within the cavity, and means within the body and inner cylindrical sleeve by which the internal cylindrical surface of the elastic Jointing sleeve is exposed to the well.

14. An internal plug for tubing in pressure wells, comprising a body, a cylindrical elastic jointing sleeve upon the body, means within the body by which the internal cylindrical surface of the sleeve is exposed to the well, and mechanical means for the lapplication of pressure outwardly upon the inner cylindrical surface of the elastic jointing` sleeve.

15. An internal plug for tubing in pressure wells, comprising a body, a coincident tubular part 100 of smaller diameter depending from the body and open at its lower externally screw-threaded end,

a cylindrical elastic jolnting sleeve upon the tubular part, the tubular part having holes therein extending therethrough by whichl the said sleeve is subject to the well pressure from below the body, and means for holding the cylindrical elastic sleeve in position against the well pressure and applying axial pressure to the said sleeve comprising a nut applied upon the lower end of the tubular part.

16. A plurality of separable internal plugs in line, for tubing in pressure wells, each plug comprising a body adapted to be closed at the upper end and having a tubular lower part and a eylindrical elastic jointing sleeve upon the tubular lower part, the tubular lower part extending downwards beyond the sleeve as a means of connection with the body of the next plug beneath and having holes therein communicating between the central cavity within the tubular lower part and the surrounding annular space beneath the sleeve, substantially as hereinbefore described.

i7. A plurality of internal plugs in line, for tubing in pressure wells, each plug comprising a body having a tubular lower part, a cylindrical elastic jointing sleeve upon the tubular lower part, the tubular lower part extending downwards beyond the sleeve as a means of connection with the body of the plug next beneath, and having near the lower end means of communication between the central cavity and the surrounding annular space beneath the sleeve, a valve in the upper part of the body, opening downwardly, and a non-return valve near the lower end of the tubular lower part above the said means of communication, the said non-return valve opening upwardly, substantially as hereinbefore described.

18. A plurality of internal plugs in line, for M@ tubing in pressure wells, each plug comprising a body having a tubular lower part and a cylindrical elastic jointing sleeve upon the tubular lower part, the tubular lower part extending `downwards beyond the sleeve as a means of connection with the body of the plug next beneath and having holes therein communicating between the central cavity within and the surrounding annular space beneath the sleeve, and a valve in the body of the uppermost internal plug, the'o said valve opening downwardly, substantially as `hereinbefore described.

ing tool into the tubing, and the releasing tool,`

substantially as hereinbefore described.

20. Means for plugging the tubing of pressure wells, consisting of a mandrel disposed above and concentric with the well head casing and adapted at its lower end for engagement, an internal plug for the tubing, elements upon the internal plug and connected thereto for connection with the lower end of the mandrel, the elements being normally subject to the action of aspring, and means consisting of a recess in the tubing bore by which the lower end of the mandrel may be released by the said elements underthe action of the said spring, substantially as hereinbefore described.

21. Means for pluggingthe tubing of pressure wells'formed of sections of tubing connected together by couplings, the bore of one of which has a greater diameter than the normal bore of the tubing, consisting of an internal plug for the tubing which comprises a body part having a number of partially cylindrical lrecesses formed at lthe top in circular series, upstanding dogs above the said body part having their lower ends of a partially cylindrical form adapted to be axially set into the said respective partially cylindrical recesses and to move pivotally therein, the outer faces of the dogs being adapted in form to that of the tubing coupling having an enlarged bore, and the upper ends of the dogs being reduced `and formed for engagement by a releasing tool and a spring by which the dogs are normally thrust outwards, substantially as hereinbefore described.

22. Means for plugging the tubing or pressure wells formed of sections of tubing connected together by couplings, the bore of one of which has a greater diameter than the normal bore of the tubing, consisting of an internal plug for the tubing which comprises a body part, upstanding dogs above the said body part and pivotally connected' thereto, said dogs having the same form and a shoulder on the outer face to engage within the tubing coupling having an enlarged bore, and having a recess on the inner side and reduced upper ends, and a spring by which the dogs are normally thrust outwards, substantially as hereinbefore described.

23. Means for plugging the tubing of pressure wells formed of sections of tubing connected together by couplings, the bore of oneof .which has a greater diameter than the normal -bore of the tubing, comprising an internal plug, dogs above the plug and connected thereto, the dogs being adapted with the plug for relative movement within the tubing and being adapted for engagement within the enlarged bore of the tubing on reaching it, and a mandrel adapted at itsl lower,

end to engage the dogs within the normal bore of the tubing, and means for supporting the mandrel in position above and concentric with the well head casing, and means for snubbing-in the sections of tubing over the mandrel, substantially as hereinbefore described.

24. An internal plug for tubing in pressure wells, comprising the tubing, a body adapted to be passed into the tubing and adapted for free movement axially within the tubing on the body being released at the well head, a cylindrical elastic jointing sleeve upon the said body, the said sleeve being accessible to the pressure in the well, and means for locating and holding the said body within the tubing, comprising a locking device upon the said body and a coupling sleeye for adjacent sections of the tubing, said sleeve having an internal diameter larger than the normal bore of the tubing.

25. An internal plug for tubing in pressure v wells, comprising, a body adapted to be passed into the tubing and to be relatively movable axially therein when released at the well head, the body having a lower tubular part, a cylindrical elastic .iointing sleeve upon the body, and means for locating and holding the said body within the tubing, comprising a locking device on the body and a coupling sleeve for adjacent sections of the tubing, said sleeve having an internal diameter larger than the normal bore of the tubing, and a valve in the upper part of the said body by which communication is open through the body.

26. Means for plugging the tubing of pressure wells, the bore of one ofk the constituents of A which tubing is enlarged to form an annular recess, comprising an internal plug having an external elastic jointing sleeve., thereon accessible tothe well pressure and a locking device above the plug and secured to it that is adapted with the plug for axial movement within the tubing ,on release at the well head, the locking device being also adapted for engagement within the annular recess in the bore of one of the constituents of the tubing on passing into it and being y the normal bore, the said internal plug and connected dogs beingadapted for free axial movement within the tubing yon release of the dogs from engagement.

28. An internal plug for tubing in pressure g wells, comprising a 'cylindrical elastic jointing sleeve, the internal cylindrical surface of which. is exposed to the well pressure, and mechanical means at the fwell head by which the internal 1,35 plug may be located and held in determined position with reference to an external packer 1ocated in the well head casing, in the running-in and withdrawal of the tubing.

29. An internal plug for tubing in pressure wells, comprising a body, part of which is of tubular form and open at its lower end, a cylindrical elastic sleeve upon the said .tubular part, an internal annular cavity ,in the sleeve, a cylindrical inelastic sleeve with the annular cav-l ity, and transverse holes extending through the tubular part of the body and the cylindrical inelastic sleeve. y

30. An internal `plug for tubing in pressure wells, comprising a body, part of which is of 150 tubular lindrical an inter lindrical form and open at its lower Lend, a cyelastic sleeve upon the said tubular part, nal annular cavity in the sleeve, a. cyinelastic sleeve within the annular cavity, transverse holes extending through the tubular pa rt of the body and the cylindrical inelasand a spring device disposed between 

